Jacky Luiten

68 | Chapter 5 histologic grade of DCIS, observed during the transition from SFM screening to digital screening, persisted several years after this transition. Materials and methods Mammography screening program and study cohort A biennial nationwide mammography screening program was introduced in the Netherlands between 1989 and 1996 for all women aged 50‐70 years. Between 1998 and 1999, the upper age limit was extended to 75 years. In the southern part of the Netherlands, SFM was gradually replaced by FFDM between May 2009 and April 2010. The Dutch screening program has been described in more detail previously. 7,12‐14 In summary, all screening mammograms are obtained by certified radiographers, after which the images are routinely double‐read by certified screening radiologists. The radiologists classify the mammographic abnormality in case of recall (suspicious mass, suspicious microcalcifications, suspicious mass in combination with microcalcifications, asymmetry, architectural distortion, or other suspicious abnormality). A Breast Imaging Reporting and Data System (BIRADS) category is routinely provided in clinical breast imaging reports after 2001. 15,16 Recalled women are then referred by their general practitioner to a hospital breast unit for further analysis. In case of a false‐positive recall, a woman returns to the screening program and is screened with the same frequency (biennial) as all other women who attend the program. We retrospectively analyzed all women who attended the breast cancer screening program at four specialized breast cancer screening units in a southern part of the Netherlands between January 1997 and January 2017. Our study population consisted of a consecutive series of 817,656 screening examinations. Women participating in the screening program were offered the option to opt out of the use of their data for quality assessment and scientific purposes. Three recalled women refrained from giving permission and were excluded from analysis. According to the Dutch Central Committee on Research involving Human Subjects, ethical approval was not required for our study. The authors declare no conflict of interest. This research did not receive any specific grant from funding agencies in the public, commercial, or not‐for‐profit sectors.